Papermaking belts are well-known in the art. Papermaking belts are used to dewater and transport cellulosic fibers in a papermaking machine. The cellulosic fibers become an embryonic web and, upon drying, the finished product.
Typically, papermaking belts do not impart structure to the paper made thereon. “Structure” refers to variations in the basis weight and/or the density of the paper which are greater than occur in ordinary papermaking and due to ordinary variations, such as those induced by creping. “Structure” may also refer to a texture or a pattern in the tissue or towel sheet. Such “structured” tissue/towel sheets are usually soft and bulky with high absorbency. Such papermaking belts may be Through Air Drying (“TAD”) belts or conventional press fabrics, transfer fabrics, or forming fabrics. Such belts comprise a surface patterning framework and may have a reinforcing structure. Structured tissue and towel can be softer, more absorbent, and be of a lower basis weight than unstructured tissue/towel. A preferred method for producing structured tissue/towel typically is Through Air Drying, which can be costly and energy intensive.
The use of impermeable belts to provide a structure to a tissue or towel sheet is also known from the art. U.S. Pat. No. 6,743,339, the entirety of which is incorporated by reference hereby, teaches the use of a smooth impermeable belt used to make tissue. U.S. Pat. Nos. 5,972,813, 6,340,413, and 6,547,924, the entirety of each of which is incorporated by reference hereby, each teach the use of an impermeable belt to provide a texture to the tissue or towel sheet. The patents explain that the impermeable belts have a measured air flow of less than 20 cfm (cubic feet per min of air passing through a square foot of belt at a one half inch water gauge pressure.) Further, U.S. Pat. No. 5,972,813 teaches that no water passes through any “capillary” having a dimension of 50 microns or greater.
The use of permeable belts with a texture is also known. U.S. Pat. No. 5,837,102, the entirety of which is incorporated by reference hereby, teaches such a belt with through holes. However the micro texture on the belt surface is only to aid sheet release.
Many presses and devices (machine apparatus) have been developed over the years to make soft, bulky structural tissue or towel in some manner. All of these devices attempt to balance the bulk properties of the structured sheet with cost and complexity. Energy and fiber costs are the two main drivers. The use of an impermeable belt is suggested to minimize energy costs as it was thought that use of a permeable belt would not lead to maximum sheet dewatering.
German Patent No. 195 48 747, the entirety of which is incorporated by reference hereby, discloses a paper machine for making creped tissue, which has a press comprising a shoe press roll, a counter roll and a suction roll, the counter roll forming a first press nip with the suction roll and a second extended press nip with the shoe press roll. A press fabric runs through the two press nips together with the paper web and then brings along the paper web to a Yankee cylinder, to which the paper web is transferred when the press fabric and the paper web pass around a transfer roll, which forms a non-compressing nip with the Yankee cylinder. Suction zones for dewatering the press fabric are available before and after the first press nip, the suction zone before the press nip located inside the suction roll while the suction zone after the press nip is located in a side loop, in which the press fabric runs alone to meet again the paper web at the entry of the second press nip. Such a paper machine is inconvenient since the paper web is rewet by the wet press fabric before it reaches the Yankee cylinder.
U.S. Pat. No. 5,393,384 (“the '384 patent”), the entirety of which is incorporated by reference hereby, discloses a paper machine for producing a tissue web, which in the embodiment according to FIG. 6 of the '384 patent comprises a non-compressible, water-impermeable belt, the underside of which conducts a paper web through a shoe press nip and from there to a Yankee cylinder, via a transfer roll which forms a nip with the Yankee cylinder. This impermeable belt has a smooth web-carrying surface which makes an adhesive water film form thereon as the belt passes through the press nip together with a press fabric which has a non-smooth surface in contact with the paper web. A Yankee cylinder has a smooth surface. As both the Yankee cylinder and the impermeable belt have smooth surfaces which the paper web is intended to contact, there is a risk that the paper web can continue to adhere to the smooth surface of the impermeable belt after having passed the nip adjacent to the Yankee cylinder instead of being transferred, as desired, to the smooth surface of the dryer cylinder. Not even if large amounts of adhesive are applied to the circumferential surface of the dryer cylinder will it be possible to ensure that the paper web adheres to the Yankee cylinder.
The production of nonwoven products is well known in the art. Such products are produced directly from fibers without conventional textile methods such as weaving or knitting operations. Instead, they may be produced by nonwoven manufacturing methods such as airlaid, drylaid, and carding, or some combination of these processes in which fibers are laid down to form an integral nonwoven web.
Nonwoven product may also be produced by airlaying, or carding operations where the web of fibers is consolidated or processed, subsequent to deposition, into a nonwoven product by needling or spunlacing (hydroentanglement.) In the latter, high-pressure water jets are directed vertically down onto the web to entangle the fibers with each other. In needling, the entanglement is achieved mechanically through the use of a reciprocating bed of barbed needles which force fibers on the surface of the web further thereinto during the entry stroke of the. needles.
There presently exists an apparatus for the production of nonwovens, for example, spunbond webs, structures or articles formed from filaments or fibers typically made from a thermoplastic rein. Such an apparatus is disclosed in U.S. Pat. No. 5,814,349, the disclosure of which is incorporated herein by reference. Such apparatuses typically include a spinneret for producing a curtain of strands and a process-air blower for blowing process air onto the curtain of strands for cooling the same to form thermoplastic filaments. The thermoplastic filaments are then typically aerodynamically entrained by the process air for aerodynamic stretching of the thermoplastic filaments, which are then after passing through a diffuser deposited upon a continuously circulating belt or screen (permeable fabric) for collecting the interentangled filaments and forming a web thereon. The web, structure or article, so formed, is then transferred and subject to further processing.
In the meltblown process for manufacturing nonwoven materials, thermoplastic polymer is placed in an extruder and is then passed through a linear die containing about twenty to forty small orifices per inch of die width. Convergent streams of hot air rapidly attenuate the extruded polymer steams to form solidifying filaments. The solidifying filaments are subsequently blown by high velocity air onto a take-up screen or another layer of woven or nonwoven material thus forming a meltblown web.
The spunbonding and meltblowing process can be combined in applications such as spunbound-meltblown-spunbound (“SMS”). In SMS a first layer of spunbonded material is formed on a belt or conveyor. The belt typically has a uniform surface pattern and air permeability to attain the right web formation during the spunbond process. The spunbonded material is deposited on the belt at the lay down forming area to form the web in a first spunbond beam.
A pressure nip, or systems such as utilizing a hot air knife can help to enhance pre-bonding pressure and/or temperature acting on the web. In order to assist in drawing the thermoplastic fibers onto the forming belt, a vacuum box is located beneath the belt and which applies suction to the belt. The airflow needed for the spunbond process is supplied to the system by a vacuum box connected to the appropriately sized vacuum pump.
An airlaid process may also be used to form a nonwoven web. The airlaid process begins with a defibrillation system to open fluff pulp. A conventional fiberizer or other shredding device may also be used to form discrete fibers. Particles of absorbent materials (for example super absorbent powder), abrasives, or other materials may then be mixed with the fibers. The mixture is then suspended in an air stream within a forming system and deposited to a moving forming belt or rotating perforated cylinder onto the circumference of which can be a metallic or polymer sleeve. The randomly oriented airformed fiber may then be bonded by applying a latex binder and drying or thermally bonding.
All these processes can use belts or sleeves which can texture or provide a texture to the nonwoven sheet produced. These belts can be permeable to air and water. Belts used, however, are produced via a woven substrate of polymeric yarns in some pattern.
Nonwoven products are generally made up of fibers locked into place by fiber interaction to provide a strong cohesive structure, with or without the need for chemical binders or filament fusing. The products may have a repeating pattern of entangled fiber regions, of higher area density (weight per unit area) than the average area density of the product, and interconnecting fibers which extend between the dense entangled regions and which are randomly entangled with each other. Localized entangled regions may be interconnected by fibers extending between adjacent entangled regions to define regions of lower area density than that of the adjacent high-density region, as the nonwoven is supported on the woven belt as it passes through the machine. A pattern of apertures substantially free from fibers may be defined within or between the dense entangled regions and interconnecting fibers. In some products the dense entangled regions are arranged in a regular pattern and joined by ordered groups of fibers to provide a nonwoven product having an appearance similar to that of a conventional woven fabric, but in which the fibers proceed randomly through the product from entangled region to entangled region. The fibers of an ordered group may be either substantially parallel or randomly disposed relative to one another. Embodiments include nonwoven products having complex fiber structures with entangled fiber regions interconnected by ordered fiber groups located in different thickness zones of the nonwoven, which are particularly suitable for apparel, including dress goods and suiting materials, and industrial products such as wipes. However, any such texture or density variations are caused by the weave pattern itself of the woven structure, subsequent processes such as embossing using mechanical rolls and pressure, or from the process itself (hydroentangling causes fiber orientation and entangling differences).